The Dilemma of the Root Apex of a Dilacerate Incisor: questions and answers

Published: July 2015

Bulletin #46 July 2015

The Dilemma of the Root Apex of a
Dilacerate Incisor: questions and answers

The long axis of an incisor tooth is described as a straight
imaginary line joining the incisal edge of its crown with the apex of its root
and it generally runs through the middle of its root canal. In the “classic”
form of root dilaceration, in which the crown and coronal portion of the root
are progressively displaced labially and superiorly in relation to the
developing apical portion of the root, the long axis becomes curved in the
sagittal plane. Dilaceration generally occurs as the result of trauma in
infancy and the most logical hypothesis that describes how this specific form
of abnormal dental development occurs, was first described in the first edition
of my book1, and reiterated in subsequent editions2, 3. It was also described in an earlier newsletter
bulletin4 on this site. The conservative orthodontic treatment of
the anomaly is dealt with in a second newsletter bulletin5.

What is the best age to treat the dilacerate incisor?

It is generally recommended that treatment of the anomaly be
performed as a phase 1 procedure, shortly after the condition has been
diagnosed, which corresponds to the time that the contralateral central incisor
and the lateral incisors on both sides have erupted, at about the age of 8
years. Certainly, treatment may be left until full eruption of all the
permanent teeth and then treated as a major part of the overall malocclusion
but, in practice, this would in any case need to be undertaken after reaching a
convenient point to pause in the treatment of the other teeth, usually when
leveling and alignment will have been achieved and a heavy main arch placed.
The treatment of the erupted teeth would be put on hold while resolving the
impaction of the incisor. Notwithstanding,
delaying treatment of the anomaly till the full permanent dentition stage means
that the child would spend an unnecessary additional 4-5 years without a front
tooth and, in the meantime, full expression of positional displacement of the
crown of the tooth will have occurred.

The final form of the dilacerate incisor sees the root
develop in the arc of a tight circle in the bucco-lingual plane and the apical
portion at right angles to the coronal portion of the root (Fig. 1).

Fig. 2a, b. Front and occlusal intraoral photographs of
patient A, a 7 year old male.

Fig. 2c. Anterior portion of the cephalogram shows the
incisal edge of the right central incisor to be located adjacent to the
anterior nasal spine and pointing upward (arrow).

Fig. 2d. The view of the tooth (arrow) in a panoramic
film. Note the end-on view of the very large pulp chamber and root canal.

Fig. 2e. A series of adjacent cone beam CT
cross-sectional cuts of the tooth to show the root curvature and the open apex.

Fig. 2f. A 3D screen shot after all bone and soft tissue
has been eliminated.

The
location of its unerupted incisal edge is usually very high up on the labial
side of the ridge close to the root of the nose, with its labial aspect facing
superiorly and posteriorly and the palatal side, including the cingulum, facing
forwards (Fig. 2). The tooth needs to be brought to its place and this involves
considerable labial root torque, which must be performed in order to align its
crown portion into alignment with the other teeth and matching its normally erupted
antimere. Achieving this will cause the root apex to point labially in contact
with and, sometimes, actually bulging the periosteum of the alveolar ridge.

Fig. 2g, h. intra-oral front and occlusal views of the
anterior dentition, showing the end of phase 1 treatment at the time of
de-bracketing.

Fig. 2i, j. Panoramic and periapical views at de-banding.

What are the factors that determine the site on the root
where the change in direction of the orientation of the apical portion of the
root begins and the acuteness of its angle?

The type of trauma that results in a “classic” dilaceration will
have attenuated or killed off all the dentine-producing cells of Hertwig’s
sheath on the sharp rim of the forming root on the labial side. This limits or
denies dentine output at that point, while the palatal side of the root continues
to churn out dentine undisturbed. Thus, the age at which the trauma will have
occurred is a critical factor. The earlier the trauma, the greater the degree
of dilaceration, simply because there is more dentinogenetic potential to be
realized post-trauma in a younger patient. No doubt the force of the trauma is
also a factor insofar as it will cause a greater or lesser area of damaged
dentine on the labial side, but this can only be conjectured.

At age 8 years, an unaffected central incisor has a wide
open apex, which is not scheduled to close until about the age of 10 years.
From the clinical perspective, it seems likely that apexification of a
trauma-affected incisor may be later than that and, at the age of 9-10 years, resolution
of the impaction and the achievement of alignment are likely to be completed before
the apex has closed. It follows, therefore, that the root will continue to
elongate along the same curved path towards the labial periosteum of the
alveolar ridge, for many months thereafter. In practice, the orthodontist will be
able to palpate this developing apex in the labial sulcus, because it will
generally create a hard protrusion disturbing the smooth continuity of its oral
mucosa covering.

Does the continued labial root torque actually cause the
root apex to perforate the labial oral mucosa?

Probably not, if it is within certain limits, but it does
make the hard protrusion highly vulnerable to traumatic injury even from
careless toothbrushing, since it has only the thinnest mucosal covering. From
this minimal ulceration, the apex, its tiny nutritive blood vessels and fragile
nerve filaments may become exposed. The mucosa is unlikely to re-heal over the
protrusion and the tooth will lose its vitality.

For this reason in many of the cases, an apicoectomy of the
root needs to be performed, usually together with a root canal filling, in
order to be sure that the remainder of the root is surrounded on all sides by
alveolar bone.

In that case, is it a good idea to fully torque the
incisor in the phase 1 treatment plan, before debanding the case?

The answer to that is the same answer that one gives to any
phase 1 case. Since the orthodontic treatment cannot be completed until all the
permanent teeth are fully erupted, the aims of early treatment should be
limited to what would otherwise be functionally or health compromised, or what
is unacceptable from the point of view of the appearance or what will worsen in
the absence of suitable treatment. For these reasons most observed
discrepancies in tooth position, rotation or axial orientation are not
attempted until a phase 2 plan is initiated in the permanent dentition. Appraised
on these criteria, the dilacerate incisor usually justifies a phase 1 treatment.
The impaction should be resolved and the tooth drawn down and aligned in the
arch. An extremely large degree of labial root torque will need to be
undertaken, but this should stop when the root end becomes mildly prominent in
the labial sulcus.6 Final root torque should only be performed
towards the end of the phase 2, when an assessment of the need for apicoectomy
will be made.

Is apicoectomy always necessary in the treatment of
dilacerate central incisors?

No, there are a good number of patients in whom the
curvature of the root end is not severe and the crown of the tooth may reach
its ideal 3D alignment in 3 places of space, without its apex bulging the
labial alveolar ridge.

Can labial root torque of an incisor with an open apex result
in a realignment of the growth direction of the developing apical portion of
the root?

The answer to this question is the same answer that needs to
be offered when asking if it is contraindicated to bodily retract maxillary incisors
in a class 2 division I case, or to apply lingual root torque of the incisors in
a class 2 division II case, in the early mixed dentition. There are no literature reports and certainly
no sound evidence of altered root morphology occurring in these circumstances,
despite the fact that root torqueing or root uprighting mechanics are performed
very frequently in everyday orthodontic practice on pre-apexified teeth. It
seems clear that the apical portion of the tooth follows a pre-determined
pattern regardless of the vectors of the forces placed on it. The common
argument that a slow “orthodontic dilaceration” of the uncompleted apical third
of the root may occur when torque is applied during the final stages of
apexification, would seem to have no basis7. On the contrary, the
fact that this unsubstantiated narrative may be false lends support to the
hypothesis explaining how dilacerations occurs, which has been reiterated here
and which is specifically based on a trauma-related etiology.

What is the reason for the frequently seen post-treatment
relapse?

When orthodontic treatment of most malocclusions is
completed, the patient is placed on a retention regime to prevent a
deterioration of the fine alignment and occlusion that will have been achieved.

At the end of a phase 1 treatment in which a dilacerate
incisor impaction has been resolved, the orthodontist is faced with a dilemma.
If no retainer is placed, the affected tooth will quickly move back out of
alignment, with the incisal edge tipping labially. This relapse is relatively
mild (Fig. 3), although its being at the front of the mouth will make it more
alarming to the patient. The reason for the deterioration, aside from the usual post-orthodontic factors, is that the
forward-facing and uncompleted root end is developing further and pushing
against the labial periosteum of the alveolar ridge. Since the periosteum is
resistant, the continued root growth pushes the formed root lingually and the
crown labially. If, therefore, retention is instituted, the apexification
process may cause the root end to bulge into the labial sulcus and require
early apicoectomy. For this reason, retention should only be maintained for as
long as there is little or no labial bulge of the developing root end and this
will require regular follow-up examination.

Should a retaining device be used at the end of the phase
1 treatment to hold the alignment until phase 2 treatment is initiated?

As with every other decision, there are pro’s and con’s. On
the one hand, the parents and child will be most distressed to see a beautiful
post-treatment alignment rapidly deteriorate, if no retainer is employed. On
the other hand, to rigidly retain in the younger patient is to find the bulge on
the labial aspect of the sulcus mucosa covering the alveolar ridge becoming
more and more prominent and vulnerable to minor traumas.

Fig. 3a, b. Intraoral frontal and occlusal views of patient
B, an 8.6 year old female showing the missing left maxillary central incisor
and space closure particularly from the tipped adjacent lateral incisor.

Fig. 3c, d. The cephalogram and panoramic views show a
similar picture of the dilacerate incisor to that of patient A.

Fig. 3e. A 3D screen shot after all bone and soft tissue
has been eliminated.

Fig. 3f. A series of adjacent cone beam CT cross-sectional
cuts of the tooth.

Fig. 3g. A series of cone beam CT axial (horizontal)
cuts. Note the change in the orientation of the tooth as the cuts progress downward
(from left to right). The 2 cuts on the extreme right show the apical part of the
root lying horizontally, with open apex and a distinct and usually palpable
bulge on the palatal side (arrows).

Fig. 3h. The end of phase 1, on the day of debonding.
Note the long clinical crown of the aligned left central incisor – an apically
repositioned attached gingival flap procedure had been advised when the incisor
had been brought down and before it had erupted, but was refused by the
parents. As a conscious decision, no retainer was placed to hold the alignment.

Fig. 3i, j. Seen 17 months later, in preparation for the
phase 2 procedure, the extent of the incisor relapse may be seen.

Fig. 3k, l. Anterior portion of the cephalogram and the
panoramic view immediately prior to the commencement of phase 2.

Fig. 3m. Following 6 weeks of orthodontic treatment, re-alignment has been achieved and there is marked improvement of the gingival
condition.

For these reasons, it is often wiser to deliberately refrain
from the temptation to produce a close to ideal result in phase 1 and to
justify this to the parents by pointing out that the child is now like any
other child who needs orthodontic treatment, but is simply too early for that
treatment. Emphasize to the parent (and note this in the records!) that a
degree of deterioration in the achieved alignment is virtually certain and that
they should expect this to occur (Fig. 3). On the plus side, the child will be
free of artificial devices in the mouth for several years hence. In cases where
there is no bulge, retention may be safely employed, with the proviso that the sulcus
be palpated every 3-6 months in the interim.

Relapse can be expected to be less after the root apex has
closed, although still appreciable due to other post-treatment destabilizing
factors. In these cases, obviously retention would be advantageous. The only
way to determine whether root development has ceased and apexification
completed is to perform a second Cone Beam CT, which is not clinically
justifiable.